Hi,
I have been going to the gym for the last 6 weeks after a break for about 12 months. I had increasing pain especially after a workout, had an MRI scan done, and found out I have Schuermanns disease of the spine. I cannot sit properly due to a bulging disc near the cocyx bone, and my back aches constantly.. Does anyone have any ideas on good exercises to help core stomach muscles, as I cannot lay on the floor, and cant do planks because of tennis elbow !.. Help !!!

Here is one you might try.
Position yourself on the floor on your hands and knees, extend one leg to the rear till your knee is straight and your leg is parallell to the floor. Return to the start and repeat with the other leg. This one my wife did for her back after an injury. Use common sense and don't perform into a range that is painful.